Just Learning

i have forged pistons in my truck and when its cold it rattles ar like a knock but when the motor gets up to tem it quites down a lot is this normal been told it is but i want other thoughts on this

99SR5

iTrader: (1)

i dont think so

drguitarum2005

i wouldn't write it off as just piston slap but it sounds like piston slap. more than likely your piston is just a *little* too small for the cylinder when cold so it has a little room for lateral movement (and thus, hits the cylinder wall) but when the engine heats up, that piston expands to fill the cylinder better. my engine does the same and it has stock pistons.

the forged pistons are less uniform in their density and thus expand/contract differently so it really doesn't surprise me

Kiwipushrod

Incorrect.




To the OP, from experience, Forged pistons are no more likely to slap then regular pistons and should actually last longer then regular pistons.

Kiwi

drguitarum2005

i got it backwards and meant the cast pistons are less uniform and expand differently...sue me. either way piston slap in our engines is common and LIKE I SAID, i wouldn't write it off as piston-slap but i would look into that as a high possibility.

either way im certainly not arguing that the forged pistons should last longer

OP: who has told you that it's normal? was it a buddy or a trusted mechanic who has looked at it?

abecedarian

how many miles (hours if you prefer, but state mean RPM) are on the engine?
were the pistons properly sized for the bore (read as: were the cylinders bored and the proper size pistons used)?
why do you have forged pistons?
what other work was done when the forged pistons went in?
what is the compression ratio of the engine?
what is the initial and total timing advance?